1. Technical Field
This invention relates to the hybridization of semiconductor devices. More particularly, it relates to a method of etching metallic contact bumps formed on component devices to remove oxide from the bumps thereby improving the reliability of the hybridized device.
2. Discussion
Recent advances in semiconductor device technology have seen the increased need to join (also referred to herein as "hybridize") two or more semiconductor component devices to each other to form a single hybridized device. To achieve high performance characteristics in hybridized devices, production methods require the ability to easily cold-weld together the metallic contact bumps of the hybridized device's individual component devices. The term "cold-welding" is known and refers to a method of joining materials together by welding them absent the application of high-temperatures. By eliminating the need for high welding temperatures, cold-welding naturally decreases thermal damage to component devices, which potentially leads to improved device performance.
Unfortunately, until the present invention, it has been difficult to reliably cold-weld semiconductor devices by applying lower weld pressures. In particular, it has been found that lower weld pressures often fail to overcome the presence of a weld-inhibiting oxide layer on the weld interface of the metallic contact bumps.
In recent years, the conventional approach to welding two component devices, each having a plurality of metallic contact bumps formed thereon, has been to apply a relatively high pressure to break the weld-inhibiting oxide layer and force the contact bumps of the two devices to weld to each other. That method is commonly employed with devices having indium bumps as the metallic contact bumps. Indium is known for its ability to form good cold-welds with itself.
Unfortunately, that technique has several drawbacks. In particular, a thin, tough oxide layer readily forms on the surface of the indium bumps. The oxide layer tends to prevent good welds at lower pressures because of excessive pressures required to break the layer so as to expose the bare indium necessary to weld. The application of excessive pressures, however, often damages the sensitive semiconductor component devices underlying the contact bumps. Additionally, application of excessive pressures has caused the bumps to deform plastically in compression, thereby reducing the bump height. As a consequence of the above problems, the reliability of the hybridized device is degraded such as by an increase in resistance at the bump interface and in some instances, the occurrence of premature physical separation of the component devices.
The application to oxidized metal of a flux compound containing deoxidizers to remove oxide layers prior to welding is known. Similarly it is known that in some non-hybridizing applications, flux is applied to indium to remove oxide formed thereon. However, the literature does not provide a teaching as to how to overcome one or more of the problems discussed above.